Radiation inspection apparatus with adjustable shutter for inspecting different sizes of tubular goods

ABSTRACT

In the new and improved radiation apparatus disclosed herein for inspecting tubular goods, a radiation detector is arranged on a selected inspection axis for receiving radiation from a uniquelyarranged radiation emitter facing the detector and rotating about the exterior of the tubular member as it is translated along the axis around the detector. In the preferred embodiment disclosed herein, this unique radiation emitter includes an array of sideby-side radioactive sources aligned with laterally-spaced focussing passages for producing a composite radiation pattern formed by a number of individual sharply-defined radiation patterns on opposite sides of the inspection axis as well as intersecting the axis. The emitter further includes a selectively-positionable radiation controller which is arranged for movement between one position for emitting only a single radiation beam of selected intensity to produce a radiation pattern of reduced size and another position for emitting radiation beams from all of the sources to produce the composite pattern across the inspection axis.

United States Patent Kahil RADIATION INSPECTION APPARATUS TUBULAR GOODS[76] Inventor: John E. Kahil, 9607 windswept,

Houston, Tex. 77042 [22] Filed: Aug. 7, 1972 [21] Appl. No.: 278,311

[52] US. Cl 250/360, 250/366, 250/494, 250/513 [51] Int. Cl. G01t 1/18[58] Field of Search 250/833 D, 336, 360, 494, 250/513 [56] ReferencesCited UNITED STATES PATENTS 2,425,512 8/1947 Crumrine 250/833 D2,486,845 11/1949 Herzog i 250/833 D 2,999,935 9/1961" Foster 250/833 D3,628,029 12/1971 Tompkins 250/833 D 3,683,186 8/1972 Tompkins 250/833 DSept. 10, 1974 Primary ExaminerJames W. Lawrence AssistantExaminerl-larold A. Dixon [57] ABSTRACT In the new and improvedradiation apparatus disclosed herein for inspecting tubular goods, aradiation detec-.

individual sharply-defined radiation patterns on opposite sides of theinspection axis as well as intersecting the axis. The emitter furtherincludes a selectivelypositionable radiation controller which isarranged for movement between one position for emitting only a singleradiation beam of selected intensity to produce a radiation pattern ofreduced size and another position for emitting radiation beams from allof the sources to produce the composite pattern across the inspectionaxis.

22 Claims, 9 Drawing Figures PAIENIED SEP 1 0 m4 SHEEI 2 0F 4 PATENIEI]SEP 1 0 I974 FIGS .L. v LATERAL DISTANCE FROM AX/S PAH-INTEDSEH 0:924

saw u or 4 722 FOLLOWER. ADDER RECORDER LATERAL D/STANCE FROM AXISAVERAGER RM RADIATION INSPECTION APPARATUS WITH ADJUSTABLE SHUTTER FORINSPECTING DIFFERENT SIZES OF TUBULAR GOODS Elongated tubular goods,such as oil-field piping or tubing and the like, are frequentlyinspected for hidden flaws and other latent defects that might causefailure of such tubular members while in service. As one aspect of theseinspections, it is often desired to also obtain representativemeasurements of wall thickness of such tubular members at spaced pointsalong their length. It will be recognized, of course, that suchthickness measurements must be obtained at several points around thecircumference of a pipe as well as along its entire length to be certainof reliably detecting imperfections.

Various thickness-measuring devices have, of course, been devisedheretofore for inspecting long lengths of pipe and tubing. For instance,one typical device of this nature employs a rigidly-interconnectedradiation detector and a radioactive source which are simultaneouslyrotated around an axially-moving pipe, with the resulting variations inmeasured radiation intensity being used to derive correspondingwall-thickness measurements along a generally-helical path around thetubular member. Although the ideal situation would be to move the pipebeing inspected slowly and rotate the radiation devices at high speed,practical considerations necessarily restrict these units to lowrotative speeds which correspondingly further limit the axial speed ofthe pipe joints and, therefore, result in inefficient inspection rates.

Alternatively, the new and improved inspection device disclosed in US.Pat. No. 3,628,029 has been found to provide accurate thicknessmeasurements of various tubular goods at efficient inspection rates. Asdescribed in that patent, a radiation detector is mounted on the freeend of a fixed, but relatively flexible, elongated lance that is alignedalong a selected inspection axis and adapted to receive a tubular memberbeing moved axially along the axis. A single radiation source issuitably mounted within an annular rotatable member adapted for rotationat high speeds around the exterior of a tubular member moving along theinspection axis. By means of a unique arrangement of convergingfocussing slots, a sharply-defined radiation pattern substantiallysmaller in area than the active portion of the radiation detector isimposed thereon. In this manner, limited lateral or vertical movementsof the radiation detector confined within the moving tubular memberbeing inspected will produce only a negligible effect on themeasurements provided by the radiation detector.

Although this new and improved inspection apparatus has proven to besuccessful in certain situations, it has been found that therelatively-large size of the detector as well as the extreme narrownessof the single radiation pattern produced thereby restricts the use of agiven unit to the inspection of tubular members only within a limitedrange of diameters. Moreover, it has been found that tubular membersbeing inspected with this apparatus have to be retained as nearly aspossible in coincidental alignment with the inspection axis of theapparatus to assure maximum accuracy. Accordingly, in view of these twolimiting factors of these prior units, the inspection of elongatedtubular members which are slightly bent or the inspection of groups ofsuch members of widely-varying diameters require special operating andhandling techniques which correspondingly reduce the efficiency of theinspection operation.

To overcome these limiting factors, another inspection device asdescribed in Patent No. 3,683,186 employs a radiation emitter having anarray of three sideby-side radioactive sources of selected intensitywhich are cooperatively mounted for rotation about an axially-movingpipe being inspected. By arranging the radiation patterns of the twoflanking sources to complement the radiation pattern of the intermediatesource, the combined patterns will enable the radiation detector to moverandomly within the pipe and still produce accurate thicknessmeasurements of the intervening pipe wall.

Still another inspection device of similar nature as disclosed in acopending patent application Ser. No. 189,306 filed Oct. 14. 1971, andalso assigned to the assignee of the present application involves asingle source which is rotated about a pipe being inspected. Ascintillation detector of unique design is cooperatively arranged toprovide a substantially uniform output as the detector moves laterallyacross the radiation beam. This particular unit is, however,substantially limited to inspection of relatively-small pipes.

Although the three inspection devices disclosed in the aforementionedpatents and application have each been highly successful, each of thesedevices are respectively limited for operation in a given range of sizesof oil-field tubular members. Thus, if a particular inspection operationrequires that a number of tubular members having a wide variety ofdiameters be tested, it has heretofore been necessary to providecompletely separate inspection units respectively equipped to handleparticular size ranges of these tubular members. The inefficiency ofthis arrangement is, of course, obvious.

Accordingly, it is an object of the present invention to provide new andimproved radiation apparatus for accurately and quickly measuring thewall thickness of elongated tubular members, such as oil-field tubulargoods, of widely-different diameters.

This and other objects of the present invention are attained by mountingradiation-detecting means on the free end of an elongated support thatis generally aligned along a selected inspection axis and adapted forreception in a tubular member moving axially along the inspection axis.Radiation-emitting means including a plurality of radiation sourcescooperatively associated with inwardly-directed focussing passagesformed within radiation-shielding means are cooperatively arranged toproduce a corresponding number of narrow radiation patterns which aredistributed transversely across the inspection axis and together form acomposite pattern of selected size and intensity. A radiation controlmask is cooperatively arranged for movement across the focussingpassages between one position where all radiation beams pass through themask and another position where less than all of the radiation beams areallowed to pass the mask. In this manner, with the mask in its oneposition, the resulting composite pattern will allow tubular members ofgiven range of relatively-large diameters to be accurately inspectedirrespective of even significant variations in either the spacing oralignment between the radiation-emitting means and theradiation-detecting means. Alternatively, with the mask in its otherposition, the resulting reduced radiation pattern will be employed forobtaining thickness measurements of tubular members of relativelysmaller diameters.

The novel features of the present invention are set forth withparticularity in the appended claims. The invention, together withfurther objects and advantages thereof, may be best understood by way ofthe following description of exemplary apparatus employing theprinciples of the invention as illustrated in the accompanying drawings,in which:

FIG. 1 schematically illustrates thickness-measuring apparatus employingthe radiation means of the present invention as it may be arranged forcooperation with typical flaw-inspection apparatus;

FIG. 2 is an elevational view, partially in crosssection, of a preferredarrangement of the thicknessmeasuring apparatus depicted in FIG. 1;

FIG. 3 is an enlarged cross-sectional view in elevation taken along thelines 33 in FIG. 2 and depicts a preferred embodiment ofradiation-emitting means arranged in accordance with the principles ofthe present invention;

FIG. 4 is a cross-sectional plan view taken along the lines 4-4 in FIG.3;

FIG. 5 depicts the radiation-emitting means of the present inventioninone operating position for inspecting tubular members of a relativelylarge size;

FIG. 6 is a graphical representation illustrating the performance of thenew and improved radiation means of the present invention when theradiation-emitting means are positioned as shown in FIG. 5;

FIG. 7 is similar to FIG. 5 but illustrates the radiation-emitting meansin another operating position for inspecting tubular members of asmaller diameter;

FIG. 8 illustrates the performance of the radiation means of the presentinvention when positioned as shown in FIG. 7; and

FIG. 9 is a schematic block diagram of a preferred arrangement ofelectronic circuitry for use with the thickness-measuring apparatus ofthe present invention.

Turning now to FIG. 1, a schematic plan view is shown ofthickness-measuring apparatus 10 arranged in accordance with the presentinvention and operatively mounted within a vehicle 11. To illustrateatypical situation in which the new and improved apparatus 10 can beadvantageously used, the thickness-measuring apparatus is depicted asbeing axially aligned with other pipe-inspection apparatus 12 such asthe flawinspection apparatus disclosed in Reissue Pat. No. 26,537. As istypical, the thickness-measuring apparatus 10 includes pipe-translatingmeans, such as a selectively-powered conveyor 13 (which may be theconveyor shown in Pat. No. 3,565,310) mounted within the vehicle 11 anda pair of portable conveyors 14 and 15 (such as those disclosed in Pat.No. 3,250,404) arranged at the opposite ends of the vehicle, forselectively moving pipe sections as at 16 back and forth through thevehicle along a generally-horizontal inspection axis 17.

Reference should be made, of course, to the aforementioned reissuepatent for elaboration of the details of the flaw-inspection apparatus12 and the particulars of its operation. However, the generalarrangement of the flaw-inspection apparatus 12 and a typical inspectionoperation therewith should be understood to better appreciate itscooperation with the new and improved thickness-measuring apparatus 10.In general, therefore, the flaw-inspection apparatus 12 is arranged tofirst progressively induce a longitudinally-oriented magnetic flux in ahorizontal pipe, as at 16, being advanced axially in a first directionalong the conveyor 13 so that transversely-oriented flaws in the pipecan be concurrently detected. Residual magnetism remaining in the pipe16 is at least partially reduced by progressively subjecting theadvancing pipe to a demagnetizing flux after it has been inspected fortransverselyoriented flaws. When the pipe 16 is also to be inspected forlongitudinally-oriented flaws, the pipe is moved onto the conveyor 14and, after being halted, subjected to a circumferentially-orientedmagnetic field. Thereafter, as the pipe 16 is returned in the oppositedirection along the inspection axis 17, it is progressively inspectedfor longitudinally-oriented flaws. On the other hand, when this latterinspection is not performed, the pipe 16 is merely returned back throughthe vehicle 11 to the conveyor 15. In either situation, however, it ispreferred that the new and improved thicknessmeasuring apparatus 10 bearranged for operation upon the return movement of the pipe 16 whetheror not the latter flaw inspection is conducted.

To perform these inspections for transverse flaws, the inspectionapparatus 10 preferably includes an annular magnetizing coil 18 havingspaced sections concentrically arranged around the inspection axis 17with a plurality of flux-detecting heads 19 arranged therebetween. Asecond annular coil 20 is also concentrically arranged around theinspection axis 17 to the rear of g the flux-inducing coil 18 andconnected to a suitable AC or pulsating DC source (not shown) forprogressively demagnetizing the pipe 16 as it leaves the fluxinducingcoil.

The flaw-inspection apparatus 12 further includes anelectrically-conductive, cantilevered elongated probe or lance 21 thatis supported at its remote end and maintained insubstantially-coincidental alignment along the inspection axis 17. Whenthe pipe 16 is to be inspected for longitudinal flaws, it is advancedonto the lance 21 and halted when the lance has passed completelythrough the pipe and its free end projects out of the rearward end ofthe pipe. To subject the pipe 16 to a circumferentially-orientedmagnetic field, a DC source 22 is connected between the remote supportedend of the lance 21 and one or more laterally-movable electricalcontacts 23 that are selectively engageable with the free end of thelance. Thereafter, as the pipe 16 is being returned, a plurality offlux-detecting heads 24 are selectively moved into contact with andcoaxially rotated about the moving pipe for detectinggenerally-longitudinal flaws therein. As previously mentioned, it ispreferred to operate the new and improved thickness-measuring apparatus10 as the pipe 16 is withdrawn from over the lance 21 whether or not thepipe is to be inspected for longitudinal flaws.

In general, as depicted in FIG. '1, the new and improvedthickness-measuring apparatus 10 is comprised of radiation-detectingmeans including one of two types of radiation detectors, as at 25 (or25' which is operatively positioned along the axis 17 and new andimproved radiation means 26 mounted on a body 27 adapted for rotationabout the inspection axis. As will be subsequently explained, theradiation means 26 of the present invention are operatively arranged foralternatively producing either a single beam of radiation or a pluralityof inwardly-directed beams of radiation of predetermined intensitieswhich are respectively distributed across a selected transverse plane topass through the wall of the pipe 16 for interception by the radiationdetector.

As illustrated in FIG. 2, the radiation detector is comprised of one orthe other of two types of detectors (or 25) which are respectivelymounted in a suitable enclosed protective housing, as at 28, that isadapted to be alternatively coupled to the free end of the elongatedprobe 21 depending upon the size of the pipe sections 16 that are to beinspected. The selection of the particular radiation detector, as at 25,will be subsequently discussed with reference to FIGS. 5 and 7. To adaptthe detector 25 (or 25) for movement relative to the lower internal wallof the pipe 16 as the pipe is axially advanced or returned along theinspection axis 17, the protective housing 28 includes a central tubularportion 29 of nylon or other solid material that will not significantlyattenuate incident radiation. In the embodiment illustrated in FIG. 2, aplurality of removable centralizing members, as at 30 and 31, are spacedcircumferentially about the end portions of the detector housing 28 forretaining the detector 25 (or 25') in general coincidental alignmentwith the inspection axis 17. As a matter of convenience, thecentralizers 30 and 31 are adapted to be readily exchanged with othermembers (not shown) of greater or lesser heights so that the new andimproved inspection apparatus 10 will be effective for inspecting a widerange of sizes of tubular members. As will be subsequently explained, byarranging the radiation means 26 to alternatively produce either asingle radiation beam for impinging on the detector 25' or a pluralityof discrete beams of radiation that are each of a reduced transversewidth somewhat less than that of the effective portion of the detector25 and distributing these beams at predetermined intervals across theplane of rotation, the radiation detector 25 or 25' will produce auniform output signal even when it is eccentrically disposed in relationto the inspection axis 17.

Accordingly, in the preferred embodiment of the thickness-measuringapparatus 10 shown in FIG. 2, the radiation detector 25 (or 25') ismounted on the free end of the lance 21 and coaxially positioned withinthe rotating body 27 which includes a horizontal, generally-tubularmember 32 having one end portion rotatably journalled within anenlarged, annular stationary housing 33 and adapted for high-speedrotation around the longitudinal inspection axis 17. The radiation means26 are eccentrically located between two longitudinallyspaced annularplates or flanges 34 and 35 secured to the unsupported or other endportion of the rotatable member 32. To dynamically balance the rotatingbody 27, a target 36 of sufficient mass is mounted between the spacedflanges 34 and 35 diametrically opposite of the radiation means 26.

As best seen in FIG. 2, the rotating body 27 is concentrically arrangedabout the horizontal inspection axis 17 and journalled within thehousing 33 by a pair of longitudinally-spaced bearings 37 and 38carrying the supported end portion of the tubular member 32. In onemanner of driving the rotating body 27 at high speeds about itsrotational axis 17, the supported end of the tubular member 32 isextended beyond the outboard bearing 37 and coupled to driving means,such as a motor 39 mounted outside of the housing 33, by a suitablepower transmission such as a typical chain or belt 40 operativelyinterconnecting a pulley 41 mounted on the tubular member and a pulley42 mounted on the shaft of the motor.

Turning now to FIG. 3, in the preferred embodiment of the presentinvention, the radiation means 26 include an array of three isotropicradiation sources 43-45 (such as Cobalt 60, Cesium 137, or otheracceptable sources of gamma radiation) which are respectively encased intypical source cups, as at 46, each having either an opening in itslower end or a reduced wall thickness through which radiation canreadily pass. The encapsulated radiation sources 43-45 are respectivelydisposed within one of three chambers, as at 47, formed side-by-side inthe upper portion of a block 48 of a suitable radiation-attenuating orshielding material. To fully enclose the sources 43-45, a removableclosure member, as at 49, is fitted into the open end of each of thesource chambers 47 and a suitable cover plate 50 is secured to theshielding block 48 over the several closure members.

The radiation means 26 of the present invention further includeparticularly-arranged radiation focussing means 51 as well asselectively-operable radiationblocking or radiation-regulating shuttermeans 52 operatively disposed between the focussing means and theradioactive sources 43-45. As best seen in FIG. 3, the focussing means51 are comprised of a second block 53 formed of steel, tungsten, lead orsome other suitable radiation-attenuating or shielding material that ismounted between the annular flanges 34 and 35 and spaced radiallyinwardly from the shielding block 48 and diametrically opposite from thetarget shield 36 (FIG. 2). The shutter means 52 are comprised of a thirdblock 54 of radiation-shielding material mounted between the shieldingblock 48 and the focussing block 53. Three generally-parallelradially-directed radiation passages, as at'55-57, which arerespectively aligned with the three radiation sources 43-45 arerespectively formed in each of the blocks 48, 53 and 54. As willsubsequently be explained in greater detail, the shutter means 52 areuniquely arranged for selectively controlling the passage of radiationfrom the sources 4345 through the radiation passages 55-57 to thedetector 25.

Of paramount significance to the present invention, it will be notedfrom FIG. 3 that the radiation means 26 also include aselectively-positionable masking member such as an elongated bar 58 ofsteel or some similar material which, in the preferred embodiment of thepresent invention, is slidably mounted between the blocks 48 and 54 forselective longitudinal movement transversely across the three radiationpassages 55-57. As best seen in FIG. 4, in the preferred embodiment ofthe masking bar 58, six openings 59-64 are provided at equally-spacedintervals along the length of the bar. with the spacing between eachadjacent set of openings being equal to one half of the transversespacing between the radiation passages 55-57. Thus, by placing themasking bar 58 in the position shown in FIG. 3, the separate,generally-parallel beams of radiation 54-67 respectively emanating fromthe radiation sources 43-45 will be directed through the openings 60, 62and 64 in the bar. On the other hand, when the masking bar 58 is shiftedto the right to the dashed-line position shown at 68 in FIG. 3, theopenings 60, 62 and 64 will be out of registration with the radiationpassages 5557 and the openings 59, 61 and 63 will instead be alignedwith these radiation passages. The significance of these alternativepositions of the masking bar 58 will subsequently be explained withreference to FIGS. and 7.

To accurately locate the masking bar 58 in either of its two alternativeoperating positions as well as to releasably secure the masking bar inthese positions, the preferred embodiment of the present inventionincludes manually-operable detent means such as a pair oflongitudinally-movable rods or bolts 69 and 70 which are mounted in theshielding block 48 and respectively disposed in elongated slots 71 and72 in the ends of the bar. Biasing means such as compression springs 73and 74 are cooperatively arranged to normally urge the bolts 69 and 70upwardly but still allow the bolts to be manually shifted downwardly asrequired to displace the lower enlarged heads 75 and 76 of the boltsbelow the lower face of the masking bar 58. By respectively providingeccentrically-located counterbores, as at 77 and 78, on the outer edgesof the slots 71 and 72, when the masking bar 58 is shifted so as toalign one of the counterbores with the head of its respective bolt, asat 69 (or 70), the enlarged head 75 (or 76) will be snugly retained inthe counterbore by the spring 73 (or 74) so as to retain the masking barin that position. The opposite result is, of course, obtained when thebolt 69 is momentarily depressed to remove the enlarged head 75 from thecounterbore 77 to permit the masking bar 58 to be shifted transverselyto its position at 68 to then align the enlarged head 76 with thecounterbore 78.

It will also be noted from FIGS. 3 and 5 that the radioactive sources4345 are uniquely arranged so that the separate beams of radiation 65-67are each directed at spaced intervals along a selected transverse planeintersecting the inspection axis 17. In particular, in the preferredembodiment of the invention, the radiation means 26 are arranged so thattwo of the three radiation beams 65 and 67 are respectively directed onopposite sides of the axis 17 and the third beam of radiation 66 willintersect the inspection axis to define a composite radiation pattern ofselected intensity and lateral width. Accordingly, as illustrated inFIG. 5, when the mask 58 is positioned as shown and the detector iscoincidentally aligned with the inspection axis 17, the radiation beam66 from the central radioactive source 44 will be directly impinged onthe detector and the exterior or flanking beams of radiation 65 and 67will substantially uniformly straddle the detector. ,On the other hand,as schematically depicted by the dashed circles 79 and 80, should thedetector 25 be shifted laterally to either side of the inspection axis17, the active portion of the detector will progressively receive moreradiation from one or the other of the two flanking beams 65 (or 67) andcorrespondingly receive a lesser amount of radiation from the centralbeam 66. The significance of this will best be appreciated by therespective response curves for the detector 25 as graphically depictedin FIG. 6.

Accordingly, as schematically represented in FIG. 6, by selecting agiven energy or intensity for the central radioactive source 44, thedetector 25 will respond to irradiation from this source as graphicallydepicted by the centrally-located response curve 81. As representedthere, so long as the detector 25 remains coincidentally aligned withthe inspection axis 17, the maximum intensity of the central radioactivesource 44 will be received thereby so as to produce the maximum outputas represented by the peak of this central response curve 81. On theother hand, lateral movement of the detector 25 to either one. side orthe other of the inspection axis 17 will progressively diminish theradiation intensity being received from the central source 44 by thedetector and produce a correspondinglyreduced output signal generally asindicated by the portions of the central response curve 81 thatasymptotically approach the distance" axis on either side of theintensity maximum. The same results will, of course, be obtained foreach of the two flanking sources 43 and 45 (FIG. 5) as shown by theirrespective response curves 82 and 83 (FIG. 6).

Accordingly, by selecting the sources 43 and 45 to have equal but lesserstrengths than the central source 44 and cooperatively arranging the twoflanking radioactive sources in the manner depicted in FIGS. 3 and 5, asthe detector 25 shifts to one side or the other of the inspection axis17, the detector will be irradiated by a combination of one of the twoflanking radiation beams, for example the left-hand beam 65, as well asthe central radiation beam 66. Thus, as shown in FIG. 6, as the detector25 moves further to the left, the progressively-increasing signal (asdepicted by the response curve 82) produced by the weaker radioactivesource 43 will be added to the progressivelydiminishing signal (as shownby the response curve 81) produced by the central radioactive source 44so as to produce a combined or composite output as represented by theoverall response curve 84. The same response will, of course, beobtained whenever the detector 25 shifts to the right-hand side of theinspection axis 17 except that the right-hand radioactive source 45 willproduce a progressively-greater output signal (as shown by the responsecurve 83) as the output signal contributed solely by the centralradioactive source 44 progressively diminishes. It will, of course, beappreciated that the strengths of the two flanking sources 43 and 45 arecooperatively selected in accordance with their lateral spacing from thecentral source 44 to obtain the additional intensity to make thecombined out put substantially constant across the expected rangeoflateral movements of the detector 25 for the larger sizes of pipe as at16.

It will be appreciated, therefore, that with the mask 58 in the positionshown in FIGS. 3 and 5, the new and improved radiation means 26 of thepresent invention will produce a substantially-uniform output signal fora given thickness of metal between the radiation sources 43-45 and thedetector 25 so as to at least minimize the effects which would otherwisebe caused by lateral shifting of the detector in relation to theinspection axis 17.

should also be noted that even though the detector 25 may bounceupwardly and downwardly (vertically as viewed in FIG. 5) as the pipe 16is being moved over the detector, the radiation means 26 of the presentinvention will also provide substantially-uniform signals over anacceptable range of vertical movement of the detector inasmuch as theradiation beams 67 are well collimated and the sides of each beam arerelatively parallel so that the flux density of each beam will besubstantially equal at different vertical positions within the expectedrange of vertical movement of the detector. Thus, the vertical movementsof the detector 25 are usually within a range where the axes of theradiation beams 6567 can be perfectly parallel and still maintain asubstantially-equal flux density within this range. It has been found,however, that by arranging the outer radiation passages 55 and 57 toconverge the flanking beams 65 and 67 slightly inwardly a few degrees,the outer radiation patterns will be moved slightly inwardly toward thecentral radiation pattern to produce a more-uniform flux density over agreater range of vertical movments of the detector 25 without reducingits range of lateral movements.

It has been found that where typical oil-filed tubular goods are beinginspected, the efficiency of the new and improved thicknessmeasuringapparatus is significantly improved where the radioactive sources 43-45are selected for producing a substantial count rate at the detector 25in the order of 10 to 10 counts/second as a tubular member is beinginspected. With count rates of this magnitude, it will be appreciatedthat the detector 25 will be operated at optimum statistical accuracy sothat pipes, as at 16, can be moved through the inspection apparatus 10at reasonably-high axial speeds without unduly compromising the accuracyof the resulting thickness measurements.

To produce such high count rates while there is an intervening pipe wallbetween the radiation means 26 and the detector 25 will, of course,cause the detector to be subjected to much-greater count rates when apipe is not positioned over the detector. It has been found, however,that with even the highest-quality radioactivity detectors, theprolonged exposure of the detector 25 to such greatly-increased countrates will rapidly cause the detector to begin drifting and that thisdrift or error is accelerated at an exponentiallyincreasing rate so longas the exposure is continued. Moreover, it has been found that evenbrief direct exposures of even a high-quality radioactivity detector tosuch greatly-increased count rates will quickly initiate unreliable orunstable operation of the detector 25 which will not be corrected untilthe detector has been inserted into a pipe for a considerable period oftime. Those skilled in the art will, of course, recognize that a typicalinspection operation cannot be reliably conducted with sufficientrapidity to always assure that the detector 25 will be inserted into apipe so as to prevent the occurrence of such unstable operation of thedetector. Such unpredictable operation of the detector 25 will,therefore, either result in unreliable measurements being obtained ormake it necessary to delay the inspection of another pipe for at least aconsiderable period of time until the radioactivity detector has againstabilized.

Accordingly, as described in more detail in US. Pat. No. 3,683,187 theshutter means 52 are operatively arranged for selectively attenuatingthe radiation beams 65-67 at all times that a pipe, as at 16, is notpositioned over the detector 25. Thus, by reducing the intensity ofradiation intercepted by the detector 25 to at least a reduced levelthat will not create the aforementioned unstability or drifting of thedetector, the new and improved thickness-measuring apparatus 10 can beoperated at efficient inspection rates without compromising the accuracyof the resulting measurements.

Referring again to FIGS. 2 and 3, it will be noted that in the preferredembodiment of the shutter means 52 employed for use in the presentinvention, a flat plate is cooperatively arranged for sliding movementwithin a complementary passage 86 formed in the shutter block 54parallel to the axis 17 and intersecting the radiation passages 5557therein. In the preferred embodiment of the thickness-measuringapparatus 10, the intersecting passage 86 is parallel to the inspectionaxis 17 and the shutter plate 85 is of sufficient length that it willproject outwardly from the forward and rearward faces of the flanges 34and 35.

As best seen in FIGS. 2 and 3, in its preferred embodiment the shutterplate 85 is appropriately sized in relation to the passage 86 so as tobe capable of movement completely out of alignment with the radiationpassages 5557 when the radiation-emitting means 26 is being used toperform an inspection operation. On the other hand, the shutter plate 85is particularly formed to have a thickness of a selected andpredetermined magnitude so that upon movement of the plate to positionthe plate in alignment with the radiation passages 5557, the radiationintercepted by the radiation detector 25 will be reduced to produce aselected count rate at the detector.

Accordingly, the new and improved thicknessmeasuring appartus 10 isoperatively arranged for selectively moving the shutter plate 85 toshift it out of alignment with the radiation passages 5557 just as theleading end of the pipe 16 approaches the detector 25 and thenrepositioning the shutter plate to bring it back into alignment with theradiation passages as the trailing end of the moving pipe passes overthe detector. It will be appreciated, therefore, that thesealternatelydirected movements of the shutter plate 85 between itsrespective positions will assure that the detector 25 will be protectedfrom exposure to excessive radiation intensities that could otherwisecreate the aforementioned problems with unstability or drifting of thedetector.

In the preferred manner of accomplishing these alternately-directedmovements of the shutter plate 85 and as disclosed and claimed in US.Pat. No. 3,684,887, rounded knobs, as at 87 and 88, are mounted on theouter ends of an elongated rod 89 coupled to the shutter plate. To allowunimpeded passage of the radiation beam 66 when the shutter plate 85 isin the position illustrated by the dashed lines at 90 in FIG. 4, anopening 91 is arranged in the actuating rod 89 to be in registrationwith the radiation passage 56 when the shutter plate is in its openposition. Since the shutter plate 85 will follow a circular path uponrotation of the rotating body 27, straps, as at 93 and 94 (FIG. 1), of arelatively-flexible material are respectively secured to the forward andrearward portions of the housing 33 and operatively arranged for pivotalmovement from first positions away from the housing to second positionsimmediately adjacent thereto which respectively intercept the paths ofrotation on the forward and rearward knobs 87 and 88.Selectively-operable solenoid actuators 95 and 96 are arranged adjacentto the straps 93 and 94, respectively, and so located that, uponenergization of the first actuator 95, the strap 93 will be moved intothe rotational path of the knob 87 and will accordingly shift theshutter plate 85 to the position illustrated in FIG. 2 before therotating body 27 completes a full revolution. Conversely, by energizingthe second acutator 96, the shutter plate 85 will be quickly shifted inthe reverse direction to its alternate position for opening theradiation passages 5557. In the preferred embodiment of thethickness-measuring apparatus 10, the selective operation of thesolenoid actuators 95 and 96 is accomplished by arranging typical limitswitches, as at 97 and 98 in FIG. 1, for contact by the pipe 16 as itpasses. along the conveyor 13 to shift the shutter plate 85 back andforth in proper coordination with the operation of thethickness-measuring apparatus.

Turning now to FIG. 7, it will be appreciated that thethickness-measuring apparatus has been adjusted for inspecting smallersizes of tubular members by shifting the masking bar 58 to the right soas to now position the openings 59, 61 and 63 in registration with theradiation passages 55-57. Moreover, as will subsequently be explained,the detector 25 has now been removed and a new and improved detector 25is now mounted on the lance 21. All other elements of the new andimproved apparatus 10 remain the same as previously described withreference to FIG. 5. As illustrated, the pipe 16 which is to beinspected is of a smaller diameter than the pipe 16.

As best illustrated in FIGS. 4 and 7, the opening 61 in the masking bar58 is unimpeded and the openings 59 and 63 are respectively plugged orblocked with members 99 and 100 of a suitable radiation-attenuatingmaterial, such as tungsten or lead, of sufficient thickness to block thepassage of most, if not all, of the two flanking radiation beams 65 and67. Thus, as depicted in FIG. 7, only the central radiation beam 66 ispermitted to emanate from the radiation means 26 for intersecting thewall of the pipe 16'. In other words, only the central radiation source44 is effective when the masking bar 58 is in the position shown in FIG.7.

It will, of course, be appreciated that it may be desired to select theradiation source 44 so that the intensity of the radiation beam 66 is ofa substantial magnitude when the masking bar 58 is in the position shownin FIG. 7 and is of a somewhat lesser magnitude when the masking bar isin the position shown in FIG. 5. Thus, in the preferred embodiment ofthe present invention, the opening 62 in the masking bar 58 is partiallyobstructed either with a slight radiation attenuator or by leaving a web101 of predetermined thickness in the opening. In this manner, theintensity of the central radiation beam 66 is somewhat reduced when themasking bar 58 is in the position shown in FIG. 5 so as to betterachieve the cooperation between the three sources 43-46 as depicted inFIG. 6.

Referring again to FIG. 7, it will be noted that the central radioactivesource 44 and the radiation passage 56 are cooperatively arranged todirect the beam of radiation 66 along a radial radiation axisintersecting the inspection axis 17. It will also be noted that, asindicated by the dashed circles 102 and 103, the detector 25' is capableof moving laterally on opposite sides of the inspection axis 17 withinthe pipe 16. Thus, only so long as the detector 25 is coincidentallyaligned with the inspection axis, will the radiation beam 66 beuniformly impinged on radiation-sensitive means, such as a scintillationcrystal 104 of unique design which is cooperatively arranged within thedetector; and, in the other positions of the detector (as at 102 and103), the

radiation beam will be unsymmetrically aligned in relation to the activeportion of the crystal. It will be appreciated, therefore, that sincethe output of the scintillation crystal 104 is directly related to theintensity of the radiation beam 66 as well as to the total effectivecrosssectional area of the active portion of the crystal which is beingirradiated at any given time. the lateral position of the detector 25'in relation to the inspection axis 17 would significantly affect theoutput of the detector as shown at 105 in FIG. 8 unless the principlesof the invention described in the aforementioned copending application,Ser. No. 189,306 are followed.

Accordingly, in keeping with the objects of the invention described inthe aforementioned application, the detector 25 is uniquely arranged toprovide a uniform output signal for a given flux of the radiation beam66 over a wide range of lateral movements of the detector within thepipe 16 on either side of the inspection axis 17. In the preferredmanner of accomplishing this unique result, the scintillation crystal104 is selectively shaped so as to make the effective volume of itsactive portion which is intersected by the radiation beam 66 when thedetector 25 is coincidentally aligned with the inspection axis 17substantially equal to the effective volume of the active portion whichis intersected by the beam when the detector is on either side of theinspection axis. Thus, as shown in FIG. 7, where the scintillationcrystal 104 is a cylinder, a longitudinal bore 106 is symmetricallyformed therein for removing a sufficient volume from the central portionof the crystal to achieve a selected reduction in the output response ofthe crystal when it is coincidentally aligned with the axis 17. As bestseen in FIG. 8, therefore, the crystal 104 is selectively hollowed in asymmetrical fashion to obtain an output response similar to thatillustrated at 107. It will, of course, be appreciated that theparticular dimensions of the axial bore 106 will be wholly dependentupon the physical size of the crystal 104 as well as the range oflateral movement of the detector 25 and the intensity and width of theradiation beam 66 at the axis 17.

Accordingly, as schematically represented in FIG. 8, at a given energylevel or intensity for the radioactive source 44, the detector 25' willrespond to irradiation from the source as graphically depicted by theresponse curve 107. As represented there, so long as the detec tor 25remains coincidentally aligned with the inspection axis 17, the maximumintensity of the radioactive source 44 will be received thereby so as toproduce the reduced output as represented by the center of the flatportion of the response curve 107. On the other hand. lateral movementof the detector 25' to either one side or the other of the inspectionaxis 17 will progressively diminish the radiation intensity beingreceived from the source 44 by the detector but a substantially equaloutput will be produced as represented by the outer portion of theflat-top curve portion. A correspondinglyreduced output signal (asgenerally indicated by the flank portions of the response curve 107 thatasymptotically approach the distance axis on either side of the curve)will, of course, be produced should the detector 25 move outwardlybeyond either of its eccentric positions 102 and 103.

It will be appreciated, therefore, that the unique radiation detector25' will produce a substantially-uniform output signal for a giventhickness of metal between the radiation source 44 and the detector soas to at least minimize the effects which would otherwise be caused bylateral shifting of the detector within the pipe 16'. It should also benoted that even though the detector 25 may bounce upwardly anddownwardly (vertically as viewed in FIG. 7) as the pipe 16' is beingmoved thereover, the new and improved radiation detector of the presentinvention will also provide substantiallyuniform signals over anacceptable range of vertical movement of the detector inasmuch as theradiation beam 66 is well collimated and the sides of the beam arerelatively parallel so that its flux density will be substantially equalat different vertical positions within the expected range of verticalmovement of the detector.

As previously mentioned with respect to the detector 25, the efficiencyof the new and improved thicknessmeasuring apparatus is significantlyimproved where the radioactive source 44 is selected for producing asubstantial count rate atthe detector in the order of 10 to lO-counts/second as a tubular member is being inspected. Hereagain, withcount rates of this magnitude, it will be appreciated that the detector25' will be operated at optimum statistical accuracy for typicalinspections. Moreover, such greatly-increased count rates will similarlyrequire the use of the shutter means 52 to assure reliable and stableoperation of the detector 25.

It will, of course, be appreciated that as far as the requirements ofthe present invention are concerned, circuitry such as that shown inFIG. 8 of US. Pat. No. 3,565,310 can be efficiently employed forobtaining adequate records with the new and improved thickness-measuringapparatus 10. In the preferred embodiment of the thickness-measuringapparatus 10, it is preferred, however, to employ new and improvedcircuitry such as schematically depicted at 108 in FIG. 9 of the presentapplication and described in greater detail in US. Pat. No. 3,683,187.As disclosed in greater detail in this last-mentioned application, thenew and improved circuitry 108 is uniquely arranged for cooperation withthe shutter means 52.

In general, the circuitry 108 is uniquely arranged so that each time theshutter plate 85 is in its radiationblocking positions, a calibrationmeasurement is made of the thickness of the plate. Then, as a pipe, asat 16 (or 16') is being inspected, the resulting thickness measurementsbeing obtained are compared with the previously-obtained calibrationmeasurement for determining the accuracy of these thicknessmeasurements.

As described in greater detail in the aforementioned patent, thecircuitry 18 is appropriately arranged for converting the output signalof the radiation detector 25 (or 25) to a meaningful record. Toaccomplish this, the output signal of the detector 25 (or 25') iscoupled by way of suitable conductors 109 and 110 and an amplifier 111to an indicator, such as a recorder 112, that is appropriately arrangedfor progressively providing a continuous first indication representativeof the wall thickness of a tubular member passing through the inspectionapparatus 10. As an additional feature, the circuitry 108 also includesa time-averaging circuit 113 appropriately tuned to average the outputof the detector 25 (or 25') for each revolution of the radiation means26 to provide a second indication, as on a typical recorder 114,representative of the transverse crosssectional metal area through thatportion of the tubular member scanned in that revolution. In thismanner, by driving the recorders 112 and 114 at speeds related to theaxial speed of the pipe 16 (or 16) past the apparatus l0, continuousmeaningful records will be obtained fo the actual metal thicknessesalong the generallyhelical inspection path around the pipe as well as ofsuccessive transverse cross-sectional metal areas along the length ofpipe. The circuitry 108 further includes alarm indicators, as at 115 and116, coupled to the recorders 112 and 114 and adapted for warning theoperator of the apparatus 10 that the representative thick ness and areameasurements are less than some selected minimum value.

To provide the aforementioned calibration measurements, the circuitry108 further includes a normallyopen relay 117 which is appropriatelyconnected to the solenoid actuator 96 and adapted to be closed when theshutter plate 85 is in its radiation-blocking position. In this manner,when the radiation passages -57 are closed, the output of the detector25 (of 25) will be temporarily coupled by way of an adder 118, afollower 119, and an adder 120 to the amplifier 111 to produce an inputsignal at the recorder 112 that corresponds to the known thickness ofthe shutter plate 85. A selectively-adjustable reference signal, such asprovided by a constant-voltage source 121 and a potentiometer 122, iscoupled to the other input of the adder 118 for accurately resetting therecorder 112 before the first pipe that is to be inspected is passedthrough the thickness-measuring apparatus 10. Once this reference signalis correctly set, the potentiometer 122 is not changed until such timethat the thicknessmeasuring apparatus 10 is again recalibrated.

For reasons that will subsequently be explained, the adder 118 is asignal-inverting adder so that the combination of the detector outputsignal and the reference signal will be inverted by the adder to providea calibration signal. The calibrated output signal from the invertingadder 118 is stored by a capacitor 123 and, by employing thehigh-impedance follower 119, will remain as a fixed input to the adder120 after the relay 117 is opened. It will be appreciated, therefore,that when the relay 117 is closed and the reference signal is applied tothe inverting adder 118, the inversion of the signals by the adder 1 18will produce an output signal from the adder 120 that equals only thereference signal. On the other hand, the signal initially stored by thecapacitor 123 will be the inverted summation of the reference signal andthe output signal of the detector 25 (or 25).

Accordingly, once the reference signal has been properly set to obtainthe correct reading at the recorder 112, the potentiometer 122 is leftalone and the first pipe, as at 16 (or 16) is inspected'As thesemeasurements are being obtained, it will be appreciated that the outputsignal of the adder 120 will be equal to the algebraic summation of thereference signal and the difference in the output signals of thedetector 25 (or 25) at that moment and at the time that the recorder 112was calibrated. Thus, the recorder 112 will, in effect, be recording thedifferences between the various wall thicknesses of the pipe 16 (or 16)and the known thicknesses of the shutter plate 85. These readings can,of course, be presented either as a true thickness measurement or as adifference between this known thickness.

Once the first pipe has been inspected, the shutter plate will, ofcourse, be reclosed and the relay 117 will again be reclosed just beforethe next pipe is inspected. At this time, if there has been drifting ofthe detector 25 (or 25'), the calibration signal that is then stored onthe capacitor 123 will be the inverted algebraic summation of theunchanged reference signal and the output signal of the detector whichwill be then produced as a result of any drifting. It will be recalledthat the potentiometer 122 is not changed. Thus, with the relay 117being reclosed, the output of the adder 120 will'again be equal to onlythe original unchanged reference signal which will indicate that thecircuitry 108 is still properly calibrated.

Once the next pipe is moved through the thickness measuring apparatus 10and the relay 117 is reopened, the resulting output signal from theadder 120 will again be equal to the algebraic summation of thereference signal and the difference in the output signals of thedetector (or 25) at that moment and at the time the second calibratingsignal was stored on the capacitor 123. Hereagain, the resulting signalrecorded by the recorder 112 will be representative of the differencesin the thicknesses of the pipe being inspected and the known thicknessof the shutter plate 85. 7

It will be appreciated that a more-precise calibration signal can bestored in the capacitor 123 if the detector 25 (or 25') is in a knownposition in relation to the radiation sources 43-45 at that time.Accordingly, in the preferred embodiment of the thickness-measuringapparatus 10, means are also provided for temporarily fixing thedetector 25 (or 25) in a selected position as the calibrationmeasurements are being obtained.

Accordingly, as more-fully explained in 1.1.8. Pat. No. 3,683,187, inthe preferred manner of accomplishing this, first and secondselectively-operable clamping devices 124 and 125 (FIGS. 1 and 2) arearranged at opposite ends of the tubular member 32 and cooperativelyarranged to secure the detector 25 (or 25) in coincidental alignmentwith the inspection axis 17 as a calibration measurement is beingobtained. In general, each of the clamping devices 124 and 125 iscomprised of an opposed pair of horizontal bars, as at 126 and 127,which are respectively disposed above and below the conveyor 13 andoperatively carried for vertical movement on suitable guides or uprights128 stationed on opposite sides of the conveyor. Suitable devices, suchas solenoid-actuators or hydraulic piston actuators as at 129 and 130,are operatively coupled to the clamping bars 126 and 127, respectively,and suitably arranged for moving the opposed bars in unison intoclamping engagement on the respective end portions of the detectorhousing 28 for coaxially positioning the detector 25 (or 25 therein whena calibration measurement is to be made. Once the-calibrationmeasurement is completed, the actuators 129 and 130 are reversed toreturn the clamping bars 126 and 127 to their normal positions so thatthe pipe 16 (or 16) can freely pass through the clamping devices 124 and125.

It will be appreciated, therefore, that the present invention hasprovided new and improved radiation apparatus for accurately and quicklymeasuring the wall thicknesses of elongated tubular members of manydifferent sizes. By arranging the new and improved radiation means toproduce a plurality of narrowly-focussed beams of radiation which aretransversely distributed across the longitudinally-directed inspectionaxis, depending upon the position of the masking means as a tubularmember is advanced along this axis and over a radiation detector, eitherone or all of the radiation beams will be intercepted thereby eventhough the detector is erratically moving and does not remain incoincidental alignment with the axis. Thus, by further selecting theseveral radioactive sources and selectively positioning the maskingmeans as described in detail herein, the output of the detector can beefficiently modified to provide a substantially-constant signal for agiven thickness of metal over a predetermined range of eccentricity fromthe inspection axis irrespective of whether the pipe being inspected islarge in diameter or relatively small in diameter.

While a particular embodiment of the present invention has been shownand described, it is apparent that changes and modifications may be madewithout departing from this invention in its broader aspects; and,therefore, the aim in the appended claims is to cover all such changesand modifications as fall within the true spirit and scope of thisinvention.

What is claimed is:

1. Apparatus adapted for alternative use with a first radiation detectoradapted for loose insertion within tubular members of a first size rangemoving longitudinally along a predetermined inspection axis and a secondsmaller radiation detector adapted for loose insertion within tubularmembers of a second smaller size range moving longitudinally along saidinspection axis and comprising:

a plurality of radiation sources arranged in a side-byside relationshippositioned exterior of a tubular member moving along said inspectionaxis;

radiation-focussing means including a radiation shield between saidradiation sources and said inspection axis and having a correspondingnumber of side-by-side focussing passages respectively aligned with saidradiation sources for directing individual radiation beams towardspatially-disposed locations on a transverse plane crossing saidinspection axis; and

radiation-controlling means cooperatively arranged between saidradiation sources and said inspection axis and including aradiation-masking member positioned for selective movement in relationto said focussing passages between selected masking positions, firstmeans on said masking member operable upon movement of said maskingmember to one of its said masking positions for passing all of saidradiation beams to produce a composite radiation pattern of a selectedintensity lying across said spatially-disposed locations on saidtransverse plane and having a lateral width greater than that of thefirst radiation detector, and second means on said masking memberoperable upon movement of said masking member to another of its saidmasking positions for passing less than all of said radiation beams toproduce a reduced radiation pattern of a selected intensity lying acrossless than all of said spatially-disposed locations on said transverseplane and having a lateral width less than that of the second radiationdetector.

2. The inspection apparatus of claim 1 wherein:

said first means include first radiation-passage means in said maskingmember adapted to be aligned with said focussing passages upon movementof said masking member to its said one masking position; and

said second means include second radiation-passage means in said maskingmember adapted to be aligned with less than all of said focussingpassages upon movement of said masking member to its said other maskingposition, and radiation-blocking means on said masking member adapted tobe aligned with the remaining ones of said focussing passages uponmovement of said masking member to its said other masking position.

3. The inspection apparatus of claim 1 wherein:

said first means include a series of radiation passages spatiallydisposed along said masking member and adapted to be respectivelyaligned with all of said focussin g passages upon movement of saidmasking member to its said one masking position; and

said second means include a radiation passage in said masking memberadapted to be aligned with one of said focussing passages upon movementof said masking member to its said other masking position, andradiation-blocking means on said masking member adapted to be alignedwith the remaining ones of said focussing passages upon movement of saidmasking member to its said other masking position.

4. The inspection apparatus of claim 3 wherein:

said one radiation passage is between said radiationblocking means.

5. The inspection apparatus of claim 3 wherein:

said first means further include radiation-attenuating means in one ofsaid radiation passages for selectively reducing the intensity of theradiation beam passing therethrough when said masking member is in itssaid one position.

6. The inspection apparatus of claim 5 wherein:

said one radiation passage is separated from said series of radiationpassages.

7. The inspection apparatus of claim 1 wherein:

said first means include a series of first radiation passages spatiallydisposed along said masking member and adapted to be respectivelyaligned with said focussing passages upon movement of said maskingmember to its said one masking position; and

said second means include a series of second radiation passagesspatially disposed along said masking member and adapted to berespectively aligned with said focussing passages upon movement of saidmasking member to its said other masking position. andradiation-blocking means in all but one of said second radiationpassages for blocking said radiation beams from all but one of saidradiation sources upon movement of said masking member to its said othermasking position.

8. The inspection apparatus of claim 7 further including:

radiation-attenuating means in one of said first radiation passages forselectively reducing the intensity of the radiation beam passingtherethrough when said masking member is in its said one maskingposition.

9. The inspection apparatus of claim 7 wherein:

said first and second radiation passages are alternately disposed alongsaid masking member.

10. Apparatus adapted for alternative use with a first radiationdetector adapted for loose insertion within tubular members of a firstsize range moving longitudinally along a predetermined inspection axisand a second smaller radiation detector adapted for loose inser- 6 tionwithin tubular members of a second smaller size range movinglongitudinally along said inspection axis and comprising:

a plurality of radiation sources arranged in a side-byside relationshipfor rotation about the exterior of a tubular member moving along saidinspection axis; radiation-focussing means including a radiation shieldcarrying said radiation sources and having a corresponding number ofinwardly-directed focus sing passages respectively aligned with saidradiation sources for directing individual radiation beams therefromtoward spatially-disposed locations on a transverse plane crossing saidinspection axis; and radiation-controlling means cooperatively arrangedbetween said radiation sources and said inspection axis and including aradiation-masking member positioned for selective movement in relationto said focussing passages between selected masking positions, firstmeans on said masking member operable upon movement of said maskin'gmember to one of its said masking position for passing all of saidradiation beams to produce on said transverse plane a compositeradiation pattern of a selected intensity and of a lateral width greaterthan that of the first radiation detector, and second means on saidmasking member operable upon movement of said masking member to anotherof its said masking positions for passing less than all of saidradiation beams to produce on said transverse plane a reduced radiationpattern of a selected intensity and of a lateral width less than that ofthe second radiation detector. 11. The inspection apparatus of claim 10wherein: there is an odd number of said radiation sources and focussingpassages with one of said radiation sources and focussing passages beingdirected along a radiation beam axis intersecting said inspection axisand the remaining ones of said radiation sources and said focussingpassages being equally disposed on opposite sides of said one radiationsource and focussing passage for distributing said radiation patternssymmetrically across said inspection axis. 12. The inspection apparatusof claim 10 wherein: said first means include first radiation passagesspatially disposed along said masking member and adapted to berespectively aligned with said focussing passages upon movement of saidmasking member to its said one masking position; and said second meansinclude second radiation passages spatially disposed along said maskingmember and adapted to be respectively aligned with said focussingpassages upon movement of said masking member to its said other maskingposition, and radiation-blocking means in all but one of said secondradiation passages for blocking said radiation beams from all but one ofsaid radiation sources upon movement of said masking member to its saidother masking position. 13. The inspection apparatus of claim 12 furtherincluding:

radiation-attenuating means in one of said first radiation passagescooperatively arranged for selectively reducing the intensity of theradiation beam passing therethrough when said masking member is in itssaid one masking position. 14. The inspection apparatus of claim 12wherein:

said first and second radiation passages are alternately disposed alongsaid masking member. 15. Apparatus adapted for inspecting tubularmembers moving longitudinally along a predetermined inspection axis andcomprising:

means adapted to support an elongated tubular member for axial movementalong a selected inspection axis;

a body of radiation-attenuating material mounted for rotation about atubular member moving along said inspection axis and carrying at leastthree radiation sources arranged in a side-by-side relationship;

radiation-focussing means on said rotatable body including a firstfocussing passage arranged therein in alignment between a first one ofsaid radiation sources and a selected point of intersection with saidinspection axis to direct an inwardly-directed narrowly-focussed firstradiation beam toward said inspection axis for producing asubstantiallyuniform reduced radiation pattern of a selected reduceddimension extending transversely across said point of intersection, andat least second and third focussing passages respectively arranged insaid rotatable body in alignment with second and third ones of saidradiation sources and on opposite sides of said first focussing passageto direct inwardlydirected narrowly-focussed second and third radiationbeams on opposite sides of said reduced radiation beam for producing inconjunction with said first radiation beam a substantially-uniformcomposite radiation pattern of a selected enlarged dimension extendingtransversely across said inspection axis; and

radiation-controlling means cooperatively arranged on said rotatablebody and including a radiationmasking member positioned for selectivemovement across said focussing passages between first and second maskingpositions, first means on said masking member cooperatively arranged forsubstantially blocking said second and third radiation beams wheneversaid masking member is in its said first masking position, and secondmeans on said masking member cooperatively arranged for substantiallypassing all of said radiation beams when ever said masking member is inits said second masking position.

16. The inspection apparatus of claim wherein:

said first means include first and second radiationattenuation meanscooperatively located on said masking member to be respectively situatedin a beam-blocking position in said second and third focussing passagesonly upon movement of said masking member to its said first maskingposition.

17. The inspection apparatus of claim 15 wherein:

said second means include radiation passage means cooperatively locatedin said masking member to be in registration with all of said focussingpassages only upon movement of said masking member to its said secondmasking position.

18. The inspection apparatus of claim 17 wherein:

said first means include first and second radiationattenuating meanscooperatively located on said masking member to be respectively situatedin a beam-blocking position in said second and third focussing passagesonly upon movement of said masking member to its said first maskingposition.

19. The inspection apparatus of claim 17 wherein:

said radiation-passage means include first, second and third ports insaid masking member respectively adapted for alignment with said first,second and third focussing passages only upon movement of said maskingmember to its said second masking position.

20. The inspection apparatus of claim 19 further including:

radiation-reducing means in said first port cooperatively arranged toselectively reduce the radiation intensity of said first radiation beamonly upon movement of said masking member to its said second maskingposition.

21. The inspection apparatus of claim 15 further including:

radiation-detecting means including a radiationsensitive elementpositioned in said transverse plane and adapted for loose reception in atubular member moving along said inspection axis for operation only whensaid masking member is in its said first masking position andcooperatively, shaped for producing uniform output signals for a givenwall thickness and material of a tubular member upon random movementstherein of said radiation-sensitive element across said reducedradiation pattern.

22. The inspection apparatus of claim 15 further including:

1. Apparatus adapted for alternative use with a first radiation detectoradapted for loose insertion within tubular members of a first size rangemoving longitudinally along a predetermined inspection axis and a secondsmaller radiation detector adapted for loose insertion within tubularmembers of a second smaller size range moving longitudinally along saidinspection axis and comprising: a plurality of radiation sourcesarranged in a side-by-side relationship positioned exterior of a tubularmember moving along said inspection axis; radiation-focussing meansincluding a radiation shield between said radiation sources and saidinspection axis and havIng a corresponding number of side-by-sidefocussing passages respectively aligned with said radiation sources fordirecting individual radiation beams toward spatially-disposed locationson a transverse plane crossing said inspection axis; andradiation-controlling means cooperatively arranged between saidradiation sources and said inspection axis and including aradiation-masking member positioned for selective movement in relationto said focussing passages between selected masking positions, firstmeans on said masking member operable upon movement of said maskingmember to one of its said masking positions for passing all of saidradiation beams to produce a composite radiation pattern of a selectedintensity lying across said spatially-disposed locations on saidtransverse plane and having a lateral width greater than that of thefirst radiation detector, and second means on said masking memberoperable upon movement of said masking member to another of its saidmasking positions for passing less than all of said radiation beams toproduce a reduced radiation pattern of a selected intensity lying acrossless than all of said spatially-disposed locations on said transverseplane and having a lateral width less than that of the second radiationdetector.
 2. The inspection apparatus of claim 1 wherein: said firstmeans include first radiation-passage means in said masking memberadapted to be aligned with said focussing passages upon movement of saidmasking member to its said one masking position; and said second meansinclude second radiation-passage means in said masking member adapted tobe aligned with less than all of said focussing passages upon movementof said masking member to its said other masking position, andradiation-blocking means on said masking member adapted to be alignedwith the remaining ones of said focussing passages upon movement of saidmasking member to its said other masking position.
 3. The inspectionapparatus of claim 1 wherein: said first means include a series ofradiation passages spatially disposed along said masking member andadapted to be respectively aligned with all of said focussing passagesupon movement of said masking member to its said one masking position;and said second means include a radiation passage in said masking memberadapted to be aligned with one of said focussing passages upon movementof said masking member to its said other masking position, andradiation-blocking means on said masking member adapted to be alignedwith the remaining ones of said focussing passages upon movement of saidmasking member to its said other masking position.
 4. The inspectionapparatus of claim 3 wherein: said one radiation passage is between saidradiationblocking means.
 5. The inspection apparatus of claim 3 wherein:said first means further include radiation-attenuating means in one ofsaid radiation passages for selectively reducing the intensity of theradiation beam passing therethrough when said masking member is in itssaid one position.
 6. The inspection apparatus of claim 5 wherein: saidone radiation passage is separated from said series of radiationpassages.
 7. The inspection apparatus of claim 1 wherein: said firstmeans include a series of first radiation passages spatially disposedalong said masking member and adapted to be respectively aligned withsaid focussing passages upon movement of said masking member to its saidone masking position; and said second means include a series of secondradiation passages spatially disposed along said masking member andadapted to be respectively aligned with said focussing passages uponmovement of said masking member to its said other masking position, andradiation-blocking means in all but one of said second radiationpassages for blocking said radiation beams from all but one of saidradiation sources upon movement of said masking member to its said othermasking position.
 8. The inspection apparaTus of claim 7 furtherincluding: radiation-attenuating means in one of said first radiationpassages for selectively reducing the intensity of the radiation beampassing therethrough when said masking member is in its said one maskingposition.
 9. The inspection apparatus of claim 7 wherein: said first andsecond radiation passages are alternately disposed along said maskingmember.
 10. Apparatus adapted for alternative use with a first radiationdetector adapted for loose insertion within tubular members of a firstsize range moving longitudinally along a predetermined inspection axisand a second smaller radiation detector adapted for loose insertionwithin tubular members of a second smaller size range movinglongitudinally along said inspection axis and comprising: a plurality ofradiation sources arranged in a side-by-side relationship for rotationabout the exterior of a tubular member moving along said inspectionaxis; radiation-focussing means including a radiation shield carryingsaid radiation sources and having a corresponding number ofinwardly-directed focussing passages respectively aligned with saidradiation sources for directing individual radiation beams therefromtoward spatially-disposed locations on a transverse plane crossing saidinspection axis; and radiation-controlling means cooperatively arrangedbetween said radiation sources and said inspection axis and including aradiation-masking member positioned for selective movement in relationto said focussing passages between selected masking positions, firstmeans on said masking member operable upon movement of said maskingmember to one of its said masking position for passing all of saidradiation beams to produce on said transverse plane a compositeradiation pattern of a selected intensity and of a lateral width greaterthan that of the first radiation detector, and second means on saidmasking member operable upon movement of said masking member to anotherof its said masking positions for passing less than all of saidradiation beams to produce on said transverse plane a reduced radiationpattern of a selected intensity and of a lateral width less than that ofthe second radiation detector.
 11. The inspection apparatus of claim 10wherein: there is an odd number of said radiation sources and focussingpassages with one of said radiation sources and focussing passages beingdirected along a radiation beam axis intersecting said inspection axisand the remaining ones of said radiation sources and said focussingpassages being equally disposed on opposite sides of said one radiationsource and focussing passage for distributing said radiation patternssymmetrically across said inspection axis.
 12. The inspection apparatusof claim 10 wherein: said first means include first radiation passagesspatially disposed along said masking member and adapted to berespectively aligned with said focussing passages upon movement of saidmasking member to its said one masking position; and said second meansinclude second radiation passages spatially disposed along said maskingmember and adapted to be respectively aligned with said focussingpassages upon movement of said masking member to its said other maskingposition, and radiation-blocking means in all but one of said secondradiation passages for blocking said radiation beams from all but one ofsaid radiation sources upon movement of said masking member to its saidother masking position.
 13. The inspection apparatus of claim 12 furtherincluding: radiation-attenuating means in one of said first radiationpassages cooperatively arranged for selectively reducing the intensityof the radiation beam passing therethrough when said masking member isin its said one masking position.
 14. The inspection apparatus of claim12 wherein: said first and second radiation passages are alternatelydisposed along said masking member.
 15. Apparatus adapted for inspectingtubular members moving longitudinally along a predetermined inspectionaxis and comprising: means adapted to support an elongated tubularmember for axial movement along a selected inspection axis; a body ofradiation-attenuating material mounted for rotation about a tubularmember moving along said inspection axis and carrying at least threeradiation sources arranged in a side-by-side relationship;radiation-focussing means on said rotatable body including a firstfocussing passage arranged therein in alignment between a first one ofsaid radiation sources and a selected point of intersection with saidinspection axis to direct an inwardly-directed narrowly-focussed firstradiation beam toward said inspection axis for producing asubstantially-uniform reduced radiation pattern of a selected reduceddimension extending transversely across said point of intersection, andat least second and third focussing passages respectively arranged insaid rotatable body in alignment with second and third ones of saidradiation sources and on opposite sides of said first focussing passageto direct inwardly-directed narrowly-focussed second and third radiationbeams on opposite sides of said reduced radiation beam for producing inconjunction with said first radiation beam a substantially-uniformcomposite radiation pattern of a selected enlarged dimension extendingtransversely across said inspection axis; and radiation-controllingmeans cooperatively arranged on said rotatable body and including aradiation-masking member positioned for selective movement across saidfocussing passages between first and second masking positions, firstmeans on said masking member cooperatively arranged for substantiallyblocking said second and third radiation beams whenever said maskingmember is in its said first masking position, and second means on saidmasking member cooperatively arranged for substantially passing all ofsaid radiation beams whenever said masking member is in its said secondmasking position.
 16. The inspection apparatus of claim 15 wherein: saidfirst means include first and second radiation-attenuation meanscooperatively located on said masking member to be respectively situatedin a beam-blocking position in said second and third focussing passagesonly upon movement of said masking member to its said first maskingposition.
 17. The inspection apparatus of claim 15 wherein: said secondmeans include radiation passage means cooperatively located in saidmasking member to be in registration with all of said focussing passagesonly upon movement of said masking member to its said second maskingposition.
 18. The inspection apparatus of claim 17 wherein: said firstmeans include first and second radiationattenuating means cooperativelylocated on said masking member to be respectively situated in abeam-blocking position in said second and third focussing passages onlyupon movement of said masking member to its said first masking position.19. The inspection apparatus of claim 17 wherein: said radiation-passagemeans include first, second and third ports in said masking memberrespectively adapted for alignment with said first, second and thirdfocussing passages only upon movement of said masking member to its saidsecond masking position.
 20. The inspection apparatus of claim 19further including: radiation-reducing means in said first portcooperatively arranged to selectively reduce the radiation intensity ofsaid first radiation beam only upon movement of said masking member toits said second masking position.
 21. The inspection apparatus of claim15 further including: radiation-detecting means including aradiation-sensitive element positioned in said transverse plane andadapted for loose reception in a tubular member moving along saidinspection axis for operation only when said masking member is in itssaid first masking position and cooperatively, shaped for producinguniform output signals for a given wall Thickness and material of atubular member upon random movements therein of said radiation-sensitiveelement across said reduced radiation pattern.
 22. The inspectionapparatus of claim 15 further including: radiation-detecting meansincluding a radiation-sensitive element positioned in said transverseplane and adapted for loose reception in a tubular member moving alongsaid inspection axis for operation only when said masking member is inits said second masking position and having an effective width less thanthat of said composite radiation pattern for producing uniform outputsignals for a given wall thickness and material of a tubular member uponrandom movements therein of said second radiation-sensitive elementacross said composite radiation pattern.